The present invention relates to a connector device for a transmission line connecting two relatively rotating members, and more particularly to a connector device for a transmission line for transferring electrical signals, optical signals, or electric power between a fixed member and a rotatable member, such as a vehicular steering system, which can make only a limited number of revolutions.
In transferring electrical signals between a rotatable member, including a steering wheel and a steering shaft of a vehicular steering system, and a fixed member, including a steering column, for example, a connector device must be provided for a transmission line which connects the rotatable and fixed members. The steering wheel can make only several turns in either direction. An electrical connector device in a vehicular steering system is disclosed in U.S. Pat. No. 4,422,699. This prior art device is an example of the connector device for the transmission line for transferring electrical signals between a fixed member and a rotatable member whose number of revolutions is finite.
The disclosed connector device comprises a movable housing attached to the rotatable member, a stationary housing attached to the fixed member, and a transmission line, such as a belt-shaped flat cable, housed in a chamber defined by the movable and stationary housing. The transmission line is wound 30 like a convolution around a steering shaft, for a plurality of turns. As the line is tightened or loosened in the chamber, the movable housing can rotate relatively to the stationary housing.
The steering connector device of this type may, for example, be applied to a transmission line which is used to transmit a starting signal to an air bag system. The air bag system, which is housed in the central portion of a steering wheel, is adapted to inflate in case of a vehicle collision, thereby preventing a driver from running against his facing structures in the vehicle. The transmission line in the chamber has one end connected to lead wires which extend from a starter of the air bag system, and the other end connected to lead wires which extend from a collision sensor mounted on the front end portion of the vehicle frame.
The connector device of this type, unlike a connector device of a slip-ring type, does not include a sliding portion which is composed of a slip ring and a brush. Therefore, it has the advantage over the slip-ring-type device that it is free from a short circuit which may be caused by metal dust produced by the sliding contact between the slip ring and the brush, and from wrong operation of the air bag system due to noise signals produced at the sliding-contact portion. Since the air bag system is the most important safety equipment, however, the connector device must be reliable and stable enough to stand prolonged use. At the same time, it is expected to be low in manufacturing cost.
Meanwhile, in the connector device of this type, the coiled transmission line is held loosely in a housing assembly, in order to permit tightening and loosening of the line. Thus, if the device is used in a structure or equipment subject to vibration, such as an automobile, the transmission line will vibrate, thereby producing noise. Such production of noise may be prevented by filling the housing assembly with grease. In such an arrangement, however, the viscosity of the grease prevents the transmission line from moving smoothly. As a result, the stress on the transmission line, as well as the necessary torque for steering wheel, increases, thus inducing snapping of the line frequently and lowering the reliability of the connector device.
If the movable housing is rotated in a direction such that the transmission line is loosened, the inner end portion of the transmission line in the housing assembly may sometimes bend sigmoidally as the movable housing approaches its rotation limit. Once it occurs, such a situation tends to appear repeatedly. In such a case, the bent portion of the transmission line is liable to snap from fatigue.
In attaching the connector device to a steering system, for example, the connector device must be adjusted so that the transmission line is located in an intermediate position between its ultimately tightened and loosened positions. In this state, the steering system is kept in its neutral position for a straight advance of the vehicle. According to the conventional connector device, however, the winding state of the transmission line cannot be detected accurately. Therefore, the connector device may possibly be attached to the steering system in a manner such that the transmission line is deviated from the intermediate position. In such a case, if the steering wheel is turned beyond the rotation limit of the movable housing, the transmission line is subjected to an excessive tension. As a result, the conventional connector device is liable to suffer snapping of the transmission line or disconnection at the junction between the transmission line and lead wires extending from the starter or the collision sensor.
If socket-type couplers are used to connect the transmission line and the lead wires extending from the starter or the collision sensor, the material and manufacturing costs of the connector device will increase. In this coupler-connection arrangement, moreover, there are three junctions; between conductors of the transmission line and female contacts of a coupler for the line, between conductors of the lead wires and male contacts of a coupler for the wires, and between the female and male contacts. If the junctions are increased in number, the quality control becomes more difficult, and the reliability of the junctions is lowered in proportion.